This invention relates to a method and an apparatus for the determination of activated sludge volume index in the activated sludge process. To be more particular, the present invention relates to a method for automatic determination of the activated sludge volume index of a mixed liquor of activated sludge obtained in the form of a single sample in the aeration state of the activated sludge process employed for the treatment of municipal sewage, organic industrial wastewater, etc. and to an apparatus for practicing said method.
In the activated sludge process, the activity of biodegration of organic pollutants is effected preponderantly in the form of a biochemical reaction which is caused in the aerator. The efficiency of the treatment, therefore, depends upon the activity, mass of the activated sludge reacted with the pollutants and optimum concentration of dissolved oxygen in the aerator. For separation of activated sludge and treated water in the final settler, the activated sludge volume index (hereinafter referred to as S.V.I.) is also utilized as the criterion for the efficient and rapid separation of the activated sludge from the treated water. Accordingly, the S.V.I. proves to constitute an important criterion in the operation of the activated sludge process. The S.V.I. is expressed in the number of ml's (volume) which is assumed by 1 g of the suspended solids in the sedimented sludge obtained by subjecting the mixed liquor of activated sludge in the aerator to sedimentation for 30 minutes. This value has heretofore been determined by a method which comprises the steps of taking fixed-volume samples of the mixed liquor of activated sludge prior to its entry into the final settler, filtering one sample through a filter paper No. 6 (standard type for quantitative analysis), drying the activated sludge lodged on the surface of the filter paper, weighing the dry activated sludge to find the concentration of activated sludge (%), separately allowing another sample to stand at rest for 30 minutes, finding the volume of the sedimented activated sludge, calculating the percentage of the found volume based on the volume of the original sample, namely the sedimentation rate (%) of the activated sludge, and performing a calculation involving said concentration of activated sludge and said sedimentation rate of activated sludge in accordance with the following formula (1). ##EQU1##
The method heretofore adopted for the determination of S.V.I. is complicated as has already been pointed out and it has been practiced substantially in a manual operation. Thus, it normally takes as much as four hours to determine the concentration and sedimentation rate of a sample of activated sludge and calculate the S.V.I. from the determined values. Moreover, the values of S.V.I. obtained by this method are subject to a fairly wide range of personal error even when the determination is carried out on the same samples. With this method, therefore, it has been difficult to obtain accurate S.V.I. values quickly. Furthermore, this method has been unable to determine both the sedimentation rate of activated sludge and the concentration of activated sludge for the same single sample, because the former is obtained by allowing the sample to stand for a prescribed length of time, finding the volume of suspended solids and calculating the percentage of the found volume based on the volume of the original sample while the latter is obtained by filtering the sample, drying the filtration residue and weighing the dry residue.
Recently, methods for automatic continuous determination of the concentration of activated sludge and the sedimentation rate of activated sludge have been proposed. (A method for the determination of the concentration of activated sludge is disclosed in U.S. Pat. No. 3,893,333, for example.) These methods are intended to determine the concentration of activated sludge and the sedimentation rate of activated sludge separately of each other. None of them is capable of automatically determining the S.V.I. of a single sample of mixed liquor of activated sludge.
An object of the present invention is to provide a method and an apparatus for S.V.I. determination, which method and apparatus are readily capable of automatically determining the concentration of activated sludge and the sedimentation rate of activated sludge of a single sample of mixed liquor of activated sludge, rapidly calculating the S.V.I. automatically from the determined values, recording the data resulting from said calculation and electrically displaying the recorded data or converting said data into electric signals to transmit to a remote place.